Currently, liquified propane gas fuel is widely utilized in devices in ordinary households. Such a device includes a high pressure gas steel cylinder, a main supply valve, a pressure reducing regulator and a low pressure pipeline connected with the gas oven, in which, the pressure reducing regulator has two functions: to transform the approximately 6 kg/cm.sup.2 (60,000 mmHg.) high pressure gas in the steel cylinder to approximately 280 or 400 mmHg. low pressure gas, and to close and contain the high pressure gas in the cylinder during a pressure reducing failure. A cause of pressure reducing failure is often simply because the user forgets to shut off the main supply valve or because foreign matters are deposited at the place of contact between the outer end of the gas inlet port in the pressure reducing regulator means and the rubber pad attached to the head of the lever-type bolt shaft for reducing pressure, or because said rubber pad is broken due to over age, thereby preventing the rubber pad from normally closing the gas inlet, so the pressure of the high pressure gas cannot be reduced to a predetermined level, but results in a gradual pressure increase in the pressure reducing chamber. At this moment, if no proper measure is taken to remove the defect, and the gas supply is still used, the low pressure pipeline will be damaged and may cause a disaster. To avoid such a defect, the conventional pressure reducing regulator is provided with an automatic pressure relief design for pressure reducing failure to automatically and immediately discharge the high pressure gas through the relief valve, whenever the pressure reduction fails and the pressure in the pressure reducing chamber is higher than the predetermined pressure. Although this design can prevent the high pressure gas from damaging the downstream low pressure pipeline, it still has the following disadvantages: (1) it is impossible to sense the pressure reducing failure and it is easy to cause disasters, if and when the gas supply is continuously used without any warning; and (2) although a relief valve is attached to the conventional pressure reducing regulator to discharge the high pressure gas from within, the gas discharged would fill up the space in the user's house, since for convenience the users often store the gas steel cylinder in their house, so this approach is still highly risky in posing threats to harm the human body or to cause fires and/or explosions as well. When the pressure reducing failure takes place during use, the high pressure gas may damage the downstream low pressure pipeline and then leak in a large amount to cause a grave disaster.